Silicon carbide (SiC) is a semiconductor with a large bandgap relative to silicon (Si), and applications to power devices, high-frequency devices, high-temperature operation devices and the like are anticipated.
There exist many polytypes of SiC, but the polytype which is used in order to fabricate SiC electronic devices for practical use is 4H-SiC. As substrates used in manufacturing SiC electronic devices, ordinarily, SiC single crystal wafers are used which are formed from bulk crystal fabricated by the sublimation method, etc., and on top of which is formed SiC epitaxial growth film constituting the active region of the SiC semiconductor device.
SiC single crystal wafers generally incorporate crystal defects called threading screw dislocations (TSD) and threading edge dislocations (TED), or basal plane dislocations (BPD), and these crystal defects may result in degradation of device properties. These dislocations are basically propagated from the SiC single crystal wafer to the SiC epitaxial film. Threading screw dislocation is primarily a dislocation where the Burgers vector which is propagated along the c-axis is nc[0001]. Threading edge dislocation is primarily a dislocation where the Burgers vector which is propagated along the c-axis is a/3<11-20>. Furthermore, basal plane dislocation is a dislocation where the Burgers vector existing on the c-plane is a/3<11-20.
On the other hand, it is known that dislocations called misfit dislocations also occur within SiC epitaxial film (see Non-Patent Documents 1 and 2). These misfit dislocations are one of the basal plane dislocations that are propagated to SiC epitaxial film, and are dislocations where elongation occurs in a direction orthogonal to the offcut direction (in the case where the offcut direction is <11-20>, it would be the <1-100> direction) of the SiC single crystal wafer in the vicinity of the interface of the SiC single crystal wafer and the SiC epitaxial film. With respect to misfit dislocations, it is considered that elongation occurs in order to alleviate stress in the vicinity of the aforementioned interface.
Furthermore, not only threading edge dislocations propagated from the SiC single crystal wafer, but also threading edge dislocation arrays may be formed in the SiC epitaxial film. Specifically, two threading edge dislocations newly generated at the time of epitaxial growth become paired, and this pair of two dislocations continuously repeats, extending in a row in the <1-100> direction in the case where the offcut direction is <11-20>, thereby forming a threading edge dislocation array. Due to occurrence of threading edge dislocation arrays, the dislocation density of the epitaxial film becomes higher than that of the single crystal wafer, resulting in degradation of crystal properties in epitaxial growth. This pair of threading edge dislocations is linked at its base in a half-loop shape by a basal plane dislocation. The existence of this half-loop was suggested in Non-Patent Document 3, but as its generative cause was unclear, a means for effectively reducing threading edge dislocation arrays was unclear,
With respect to the aforementioned basal plane dislocations, it is known that they lower reliability in switching devices, and it would be desirable to reduce them. Moreover, threading edge dislocation arrays are edge dislocations that are newly generated in epitaxial film, and when the dislocation densities of the epitaxial film and the SiC single crystal wafer are compared, the dislocation density of the epitaxial film is higher due to these threading edge dislocation arrays. Consequently, it would be desirable to reduce them from the standpoint of achieving higher quality of the epitaxial film
Non-Patent Document 1: X. Zhang, S. Ha, Y. Hanlumnyang, C. H. Chou, V. Rodriquez, M. Skowronski, J. J. Sumakeris, M. J. Paiseley and M. J. O'Loughlin, J. Appl. Phys. 101 (2007) 053517.
Non-Patent Document 2: H. Jacobson, J. P. Bergman, C. Hallin, E. Janzen, T. Tuomi and H. Lendenmann, J. Appl. Phys. 95 (2004), 1485.
Non-Patent Document 3: S. Ha et al., Journal of Crystal Growth 262 (2004), pp. 130-138.